1. Field of the Invention
The present invention relates generally to an internal combustion engine intended to reduce harmful components of engine exhaust gases and, more particularly, to a torch ignition type internal combustion engine having main and auxiliary combustion chambers, in which a lean air-fuel mixture in the main combustion chamber is ignited by a torch or torches produced by the combustion of a rich air-fuel mixture in the auxiliary combustion chamber adjacent to electrodes of a spark or ignition plug.
2. Description of the Prior Art
In the applicants' prior copending application referred to above, there is disclosed a torch ignition internal combustion engine which comprises a cylinder, a piston, a cylinder head cooperating with the cylinder and the piston to define a main combustion chamber for the combustion of a lean air-fuel mixture, an intake port for introducing principally air or a lean air-fuel mixture to the main combustion chamber, an intake valve movably positioned with respect to the intake port, and an auxiliary combustion chamber formed of a pot-shaped cavity having at least one suction aperture through which a rich air-fuel mixture is supplied to the auxiliary combustion chamber when the intake valve is opened. The cavity also has at least one discharge aperture. The auxiliary combustion chamber is always communicated through the suction and discharge apertures with the main combustion chamber during the time when the intake valve is closed. The auxiliary combustion chamber is adapted to be communicated with the intake port through the suction aperture and through a part of the main combustion chamber when the intake valve is opened. A spark plug has a set of electrodes exposed to the auxiliary combustion chamber. The engine is also provided with means for introducing the rich air-fuel mixture into the auxiliary combustion chamber through the suction aperture when the intake valve is opened. The introducing means includes a fuel injection nozzle provided upstream of the intake valve for discharging a fuel at a pressure higher than the atmospheric pressure. The fuel and air in the intake port form the rich air-fuel mixture which, when the intake valve is opened, is introduced through the suction aperture into the auxiliary combustion chamber. When the rich air-fuel mixture is ignited in the auxiliary combustion chamber by the spark plug, torch jets run through the suction and discharge apertures into the main combustion chamber to ignite the lean air-fuel mixture therein.
Compared with the use of carburetors in this type of internal combustion engines, the use of fuel injection nozzles is advantageous in that a fuel can be more uniformly supplied to respective engine cylinders and in that quick response can be obtained at a transition point of engine operation, for example, at acceleration, deceleration or the like.
Through extensive researches, the inventors have found that the fuel injection timing greately influences the formation of a stratified charge of fuel in an engine cylinder, the torch ignition of the fuel charge therein and the engine performance. The term "fuel injection timing" used herein means a timing when the fuel injection ceases. In order to effectively form a stratified charge of fuel in an engine cylinder, it is indispensable that a quantity of fuel is discharged from an injection nozzle in an intake stroke of the engine. However, because a charge of fuel injected from the nozzle during the intake stroke is not easily atomized, the injection of fuel during the intake stroke gives rise to a poor combustion of the fuel with a resultant increase in the unburnt components of the engine exhaust gases. The injection of the fuel during the intake stroke is also liable to cause a part of the injected fuel to enter the auxiliary combustion chamber while the fuel is still in the form of droplets which tend to cause the plug electrodes to get wet with the fuel droplets with resultant misfire and inoperability of the engine. On the other hand, the injection of the fuel from the nozzle during the time when the intake valve is closed affords the injected fuel a sufficient time for atomization by the time the intake valve is opened. In this case, however, the atomized fuel is diffused into the air or the air-fuel mixture in the intake port and diluted thereby, making it impossible for the auxiliary combustion chamber to receive a charge of an air-fuel mixture rich enough for spark ignition.